public class MyLinkedList {
    public static class ListNode {
        public int val;
        public ListNode next;
        public ListNode prev;

        public ListNode(int val) {
            this.val = val;
        }
    }
        public ListNode head;
        public ListNode last;

        //头插法
        public void addFirst(int data){
            ListNode cur = new ListNode(data);
            if (head == null){
               head = last = cur;
               return;
            }
            cur.next = head;
            head.prev = cur;
            head = cur;
        }

        //尾插法
        public void addLast(int data){
            ListNode cur = new ListNode(data);
            if (head == null){
                head = last = cur;
                return;
            }
            last.next = cur;
            cur.prev = last;
            last = cur;
        }

        //任意位置插入,第一个数据节点为0号下标
        public void addIndex(int index,int data){
            if (index < 0 || index > size()){
                System.out.println("所输入index信息错误");
                return;
            }
            if (index == 0){
                addFirst(data);
                return;
            }
            if (index == size()){
                addLast(data);
                return;
            }
            ListNode cur = head;
            for (int i = 0; i < index ; i++) {
                cur = cur.next;
            }
            ListNode newNode = new ListNode(data);
            newNode.next = cur;
            newNode.prev = cur.prev;
            cur.prev.next = newNode;
            cur.prev = newNode;
        }

        //查找是否包含关键字key是否在单链表当中
        public boolean contains(int key){
            ListNode cur = head;
            while(cur != null){
                if (cur.val == key){
                    return true;
                }cur = cur.next;
            }return false;
        }

        //删除第一次出现关键字为key的节点
        public void remove(int key){
            if (head.val == key){
                head = head.next;
                if (head != null){
                    head.prev = null;
                }
                return;
            }
            ListNode cur = head.next;
            while(cur != null){
                if (cur.val ==key){
                    if (cur.next != null){
                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;
                    }else{
                        cur = cur.next;
                    }
                    return;
                }cur = cur.next;
            }
        }

        //删除所有值为key的节点
        public void removeAllKey(int key){
            if (head.val == key){
                if (head.next != null){
                    head.next.prev = null;
                }
                head = head.next;
            }
            ListNode cur = head;
            while(cur != null){
                if (cur.val ==key){
                    if (cur.next != null){
                        cur.next.prev = cur.prev;
                    }else {
                        cur.prev.next = null;
                        last = last.prev;
                    }
                    if (cur.prev != null){
                        cur.prev.next = cur.next;
                    }else {
                        head = head.next;
                    }
                }cur = cur.next;
            }
        }
        //removeAllKey的另一种解法如下：
        /*public void removeAllKey(int key){
            if (head.val == key){
                if (head.next != null){
                    head.next.prev = null;
                }
                head = head.next;
            }
            ListNode cur = head;
            while(cur != null){
                if (cur.val ==key){
                    if (cur.next != null){
                        cur.next.prev = cur.prev;
                    }else {
                        last = last.prev;
                    }
                    if (cur.prev != null){
                        cur.prev.next = cur.next;
                    }else {
                        head = head.next;
                    }
                }cur = cur.next;
            }*/

        //得到单链表的长度
        public int size(){
            int size = 0;
            ListNode cur = head;
            while(cur != null){
                size++;
                cur = cur.next;
            }
            return size;
        }

        public void display(){
            if (head == null){
                System.out.println("该链表为空链表");
                System.out.println();
                return;
            }
            ListNode cur = head;
            while (cur != null){
                System.out.print(cur.val + " ");
                cur = cur.next;
            }
            System.out.println();
        }

        public void clear(){
            ListNode cur = head;
            while(cur != null){
                ListNode curN = cur.next;
                cur = null;
                cur = curN;
            }
        }

    }

